Directional acoustic logger apparatus and method

ABSTRACT

An acoustic logging apparatus and method are disclosed for determining the direction of a subsurface noise source, such as a blowout well or fluid channeling behind well casing. The apparatus comprises cylindrical piezoelectric crystal transducers processed to buck each other. The method employs such an apparatus and includes generating and observing output from the crystals. The direction of the noise relative to the position of the apparatus is indicated by determining the position of the crystal transducers when their phase and amplitude differences are at a minimum. The transducer leading in phase at a point perpendicular to said position is the transducer closest to the noise source and is used to indicate the absolute direction of the noise.

FIELD OF THE INVENTION

This invention relates to a directionally sensitive noise loggingapparatus and method particularly useful in operations related to oiland gas wells.

BACKGROUND OF THE INVENTION

The practice of acoustical well logging is well known in the oil and gasindustry. One particular use of acoustic logging is to determine thepoints at which fluid or gas are entering or leaving the bore of a well.This information is particularly valuable when fluid or gas is enteringor leaving the well through a leak in the casing. These casing leaksmust often be plugged to assure proper well operations. Acoustic loggingis also useful in determining whether or not there is channeling betweendifferent producing formations in a well.

One apparatus for locating leaks in casings and boreholes is disclosedin U.S. Pat. No. 2,210,417 issued Aug. 6, 1940 to Kinley. Kinleydiscloses a sound detector suspended from a cable so that it may belowered into and withdrawn from a borehole. The detector comprises asound detecting mechanism, such as a microphone, which responds to soundproduced by the leaking liquid.

Another apparatus for determining the location of fluid entering orexiting a well is disclosed in U.S. Pat. No. 2,361,458 issued on Oct.31, 1944 to Converse. This patent discloses an acoustic device having asharp response to horizontal signals. Because of this responsecharacteristic, the apparatus may be used to very precisely determinethe points of entrance of fluid into a borehole. The apparatus ischaracterized as being sensitive to noises originating adjacent to theapparatus, while the effect of other noises in the same acousticalrange, but vertically removed from the apparatus, is substantiallyeliminated.

Although devices for determining the location of a leak in a well suchas those described above are well known, such devices are generallydirectionally insensitive. These devices identify only the depth atwhich the noise associated with the leak is being produced, not thedirection from which the noise is coming. Information as to thedirection in which a subsurface noise source is located can be veryuseful in oil and gas well operations.

One such use for directional noise information is in blowout relief welloperations. One method of correcting a blowout is to drill relief wellsto the vicinity of the well in the formation which is producing fluidsor gas into a blowout. Determining the location of such production anddrilling a relief well with the required accuracy are difficult tasks.One common technique relies on detecting aberrations in the propagationof magnetic waves in the earth. Such aberrations may be caused by thewell casing of a blowout well. Another common technique detectsresistivity differences between a blowout well casing and the earth.Such techniques can often be difficult to apply and in any event are oflittle use when a blowout occurs below the well casing or occurs in awell having no well casing.

Directional information is also useful in operations involving wellswhere channeling is occurring between different formations. Channelinginvolves the flow of fluids behind the well casing. Channeling mayinvolve the leakage of fluid or gas from a producing to a non-producingformation, or the leakage of non-hydrocarbons into a producingformation. Such leakage may result in an eventual decrease in productionfrom the well. One method of correcting such leaks is to perforate thewell casing and force cement into the undesired channel, thus blockingthe flow of fluid or gas through the channel. Although the depth atwhich the perforation should be made may be determined usingconventional noise logging techniques, the proper circumferentiallocation in which to perforate the casing is difficult to determine.

There continues to be a need in the oil and gas industry for improvedapparatus and methods for determining the direction of a subsurfacenoise source.

SUMMARY OF THE INVENTION

The directional noise logging apparatus of the present inventionincludes two cylindrical piezoelectric crystals having outputs which areelectrically processed so that the crystals buck each other. That is,the output of the crystals are electrically processed so as to opposeone another. These crystals, which are well known in the art, convertsound energy into electrical energy. The output of each crystal is asignal whose voltage is proportional to the strength of the sound energyimpinging on the crystal.

For operation, the crystals are positioned substantially side by sidewithout touching and with their cylindrical axes substantially parallelto each other. They are held in this position by epoxy, support arms orother means of rigid support. The crystals and their support are adaptedfor lowering into a borehole by attachment to or inclusion in a loggingassembly on a wireline.

In practicing the method of the present invention, the relativedirection of an underground noise source may be determined by loweringon a wireline into a borehole a logging assembly including a directionalacoustic logging apparatus having two crystals electrically processed tobuck each other. These crystal transducers are positioned with respectto each other in the apparatus so that they are side by side with theircylindrical axes substantially parallel. At the desired depth, theapparatus is rotated through 360 degrees and the crystal transducersgenerate output which is used to determine the relative direction of thenoise source. When the desired depth is substantially on the horizontalplane on which the noise source also substantially lies, the noisesource will lie on a line substantially perpendicular to that line whichmay be drawn through the centers of both transducers when their phaseand amplitude output is at a minimum. The direction of the noise sourceon this line may be determined by observing which transducer is leadingin phase when the transducers are positioned so that a line may be drawnthrough both their centers and through the noise source. Such transducerleading in phase will be the one closest to the noise source.

In practicing one application of the method of the present invention,the directional acoustic logging apparatus is lowered into the well,along with an absolute directional indicator such as a gyroscope ormagnetometer. Once at the desired depth, the directional acousticlogging apparatus and absolute directional indicator are rotated through360 degrees. During this revolution, both the directional acousticlogging apparatus and absolute directional indicator generate outputwhich is observed and preferably transmitted to recording devicespreferably on the surface. Preferably, both the phase and amplitude ofeach crystal response of the apparatus of the present invention arerecorded. These phase and amplitude measurements may be used todetermine the direction of the source of the noise which resulted inthose measurements relative to the position of the apparatus when themeasurements were taken. These measurements may then be correlated withthe indications from the absolute directional indicator to determine theabsolute direction in which the noise source is located.

In practicing another application of the method of the presentinvention, particularly an application for channel repair, the absolutedirectional indicator is replaced by a perforating gun with zero phasedshots, i.e., with shots aligned along the axis of the gun so that allthe shots are facing in the same direction. The gun is associated withthe crystals such that one crystal is aligned with the shots of the gun.This orients the shots to the noise direction when the gun isdischarged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the arrangement of the piezoelectric crystaltransducers of the present invention.

FIG. 2 illustrates the use of the apparatus of the present invention ina borehole.

FIG. 3 represents a typical plot of amplitude signals from thedirectional noise logger of the present invention.

FIGS. 4a and 4b illustrate the relationship of a subsurface noise sourceto the crystal transducers of the present invention.

FIG. 5 illustrates the use of the apparatus of the present invention inoperations to stop leakage between formations behind the casing of awell.

FIG. 6a and 6b show an alternate embodiment of the directional noiselogger of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

I have found a logging apparatus and method for determining thedirection from which a subsurface noise, such as the flow of fluid orgas through a channel, emanates. Such flow may be due, for example, tochanneling of fluids behind a well casing or to leaks in the casingthrough which fluid enters or leaves a well. The subsurface noise mayalso be due to a blowout in a well. An advantage of this invention isthat it can be used to determine the direction of the noise whether thenoise is adjacent to the borehole in which the apparatus of theinvention is employed or is some distance away, for example, as much as100 feet or more. Such determination is related to the noise itself andis not dependent on the presence near the noise source of well casingsor well tools which may be detected with magnetic or resistivitytechniques.

Application of this.invention allows the point of fluid channeling orleaking to be easily and accurately detected so that effective measuresmay be taken to stop such channeling or leaking. For example,directional noise measurements made or taken with this invention canprovide the information needed to properly orient perforations into acasing at a point of fluid channeling so the channels can be plugged.Application of this invention also allows the direction from which asource of production is coming into a blowout to be determined from arelief well. The relief well can then be more accurately drilled to asatisfactory location near that source.

The apparatus of the present invention as depicted in FIG. 1,directional acoustic logger 10, comprises two cylindrical piezoelectriccrystal detection transducers 11a and 11b. These elements operate on thewell-known principle that certain crystals produce a surface potentialdifference, or voltage, when they are stressed in appropriatedirections. Cylindrical piezoelectric crystals, or crystal transducersas they may also be called, are commonly used in borehole acousticdetection apparatus.

It is desirable in practicing this invention that the crystals be spacedas far apart as possible and still be able to fit in a borehole withoutbeing so close to the side of the hole as to result in signalinterference from extraneous acoustic paths.

In the preferred embodiment of directional acoustic logger 10, the twotransducers 11a and 11b are spaced so that the cylindrical axes of thetwo transducers are about six and one-half centimeters apart. With thisspacing the apparatus will function properly in response to acousticwaves having frequencies as low as 1000 Hz and probably somewhat lower,while still providing a device compact enough to be used in boreholes ofrelatively small diameter, for example, 8 inches.

Transducers 11a and 11b may be encapsulated in an epoxy block (notshown) so as to maintain the desired spacing. It is preferable that theepoxy selected have a high sonic velocity of approximately 5000 ft./sec.so that the phase differential measurements which are discussed belowwill be independent of influence from the presence of fluid in theborehole. At this velocity, the maximum phase differential is thatcorresponding to about 50 microseconds lag time. If an epoxy block isnot used, other support should be used to hold the crystals in place.The crystals and their support may be referred to as a transducerassembly 28.

Transducers 11a and llb are each about one-half inch in diameter and oneinch in length. The size of the transducer is not, however, particularlysignificant and any practicable size for fitting into a borehole may beused. The transducers are, however, preferably the same size and do nottouch each other when their output is being observed.

The output from transducers 11a and 11b are electrically processed so asto preferably preserve the true phase and amplitude of each output. Thesignals are further processed so as to determine the phase differencebetween the signals. This processing can be done in numerous ways knownto those skilled in the art of electronics. A novelty of this inventionlies in the significance of those two angular positions at which thetransducer signals are in phase. This significance is explained belowwith reference to the simplest procedure for detecting these in-phaselocations.

The transducers 11a and 11b are connected so as to "buck" each other. Inthe simplest arrangement, for example, this bucking may be achieved byconnecting the positive output terminal of the first crystal to thenegative output terminal of the second crystal. However, in the practiceof this invention, it is preferable that phase and amplitude output ofeach transducer be preserved. Thus, processing beyond the simplestarrangement is usually desirable. For example, as shown in FIG. 1,positive output lead 12a of transducer 11a is electrically connected tothe positive input of an operational amplifier 17 while the positiveoutput lead (12b ) of transducer 11b is electrically connected to thenegative input of the same amplifier 17. The output from the amplifier17 is fed to measurement and recording means (not shown) over wire 18.Negative output leads 13a and 13b from transducers 11a and 11brespectively are connected to lead 14 which is a ground for the system.The significance of processing the transducers in such a manner will bediscussed below.

FIG. 2 depicts the directional logger of the present invention as it maybe used in operation. The logger 10 will be positioned in or attached toa conventional logging assembly 21 and lowered into borehole 15 onelectric wire line 16. preferably blocks of acoustic isolating epoxy 22and 23 or epoxy containing lead will be above and below the transducerassembly 28 in the logging assembly 21 to prevent interference fromextraneous noise. A device which provides an indication of absolutedirection 20, such as a magnetometer or gyroscope, is in this particularapplication depicted also positioned in the logging assembly 21 andassociated to the transducers of the logger 10 in such a way that theposition of the transducers with respect to the absolute directionindicator 20 is known. Absolute direction indicator 20 will provide anindication of absolute direction during operation of logger 10. Thesignals from logger 10 are transmitted by means of electric wire line 16to phase recorder 25 and amplitude recorder 26 located at the surface27. The output signal from absolute direction indicator 20 istransmitted over electric wire line 16 to absolute direction recorder30. Although the recorders 25, 26 and 30 are located at the surface 27,they could also be located in the borehole nearer the logger 10. Asurface location for the recorders, however, is generally consideredmore convenient.

One use or example operation of directional acoustic logger 10 is in thedetermination of the direction of a noisy blowout from a remote reliefwell. It is desirable to be able to determine the direction of theblowout from the relief well so that the relief well may bedirectionally drilled to the proper location to kill the blowout.Referring again to FIG. 2, in practicing the method of the presentinvention, directional logger 10 is lowered into borchole 15, the reliefwell, on electric wire line 16 to each measurement station. At eachstop, the output of each crystal transducer is monitored on amplitudemonitor 31 on the surface 27 to determine the depth at which the peaknoise amplitude occurs. The logger is then moved to that depth where itsvertical movement is stopped. At that depth, the output from theoperational amlifier bucking the transducers is introduced to theamplitude recorder 26, and the logger 10 and the absolute directionindicator 20 are rotated 360 degrees through the horizontal plane usinga conventional downhole rotator. Such rotator may be, for example, asdepicted in FIG. 2, a barrel with a rotation motor 32 on a conventionallogging assembly 21 with centralizing bow springs 36 and 38. Electricalconnections for operating the rotation motor may be contained in thecable head 39. Both the amplitude of the bucked signal and the phase ofthe indivioual signal from transducers 11a and 11b are recorder onrecorders 25 and 26 t the surface during the 360 degree rotation. Thecorresponding signal from absolute direction indicator 20 is alsorecorded at the surface.

FIG. 3 shows actual example output of a bucked amplifier with 2 KHzinputs from the logger of this invention located in a second well, suchas a relief well, drilled 100 feet from the well containing the noisesource, such as a blowout. In this example, only amplitude for thelogger at two different vertical locations in the well is shown. Whilephase is not shown, such output would be similar, with two points at azero baseline corresponding to A₁, and A₂. However phase would appear asa sine curve. FIG. 3 shows that stronger output is seen when the loggeris directly across or on the same horizontal line or plane as the noisesource, that is, at position 1. The fact that the logger is effective atthis distance of 100 feet is significant since directional loggerscommonly used in the industry are not generally effective at this greata distance and accurate noise direction detection at such a distance isoften needed and can be very useful.

The recorded amplitude signal out of the bucked transducers asillustrated by FIG. 3, will typically be found io have two maximums orhigh points ideally 180 degrees apart, and two minimums or low pointsalso ideally 180 degrees apart. Because resonance in the borehole mayresult in the maximums of the output signals being extremely distorted,the signal minimums are used in making the actual determination of thedirection of the source of the noise. These minimums, identified by A₁and A₂ in FIG. 3, can be precisely determined by precise phase detectioninstrumentation well known to those in the field of electronics.

Because the output signals of the two individual transducers of thedirectional logger are connected so as to buck each other, the minimumamplitude and phase difference signals as recorded at the surface willoccur when, as shown in FIG. 4A, the transducers 11a and 11b areoriented so that a line 33 drawn through the centers of the twotransducers is substantially perpendicular to the direction of the noisesource 34 being detected. In this alignment, the acoustic signalsreceived by the two transducers are in phase, and as such, thetransducer outputs are in phase. Since the transducer outputs areconnected in a bucking configuration, the individual transducer outputswill tend to cancel each other. Thus, both the amplitude and phaserecorders will indicate a minimum in this alignment. These minimums arethen correlated with the corresponding point on the absolute directionrecording. A perpendicular line 35 may then be plotted in the absolutedirection associated with the two low points. The noise source beingdetected by the directional logger lies generally on this line 35.

Resonance due to borehole irregularity may cause the minimums, A₁ andA₂, FIG. 3, to be separated by more or less than 180°. An equalcorrection to each location so as to make the separation exactly 180°leads to the correct orientation of the direction line 35.

Having determined the line on which the noise source lies, the phasedifference with the transducer axis aligned on that line may be used todetermine in which direction on that line the noise source is located.Referring to FIG. 4B, when the two transducers 11a and 11b of thedirectional logger are aligned so that a line 37 drawn through thecenters of the two transducers will pass through the source 34 of thenoise being detected, the acoustic signal being received by transducer11b nearest the noise source will be out of phase with the acousticsignal being received by transducer 11a farthest from the noise source.Because the acoustic signal first impinges on the transducer closest tothe source of the noise, the direction of the noise source from thelogger on line 37 may be determined by determining which transducer'soutput is leading in phase. The phase record is used to determine whichtransducer's output is leading in phase. This phase difference is notnecessarily the maximum value recorded during the 360° rotation due tointerference from borehole irregularity. Thus, in practicing this methodof the present invention, the line on which the noise source is locatedis first determined by locating a line which corresponds to the lowpoints of the amplitude and phase output signals of the logger. In FIG.4A, this line is line 33. The direction line (line 35 in FIG. 4A) isoriented 90° to the minima axis (line 33 in FIG. 4A). The direction ofthe noise source on that line is then found by determining which of thetwo transducers' outputs is leading in phase.

The directional logger may also be used in operations required whenfluid or gas from one formation is traveling behind the casing toanother formation. Referring to FIG. 5, directional logger 40 is shownin well 49. As shown, well 49 is Producing hydrocarbons from formation54. The hydrocarbons flow into well 49 through perforations 24 in casing48. The hydrocarbons flow to the surface 19 through production tubing50. Packer 51 prevents the hydrocarbons from flowing in the annulus 52between production tubing 50 in casing 48.

A channel 55 is shown on the outside of casing 48 between formation 54and formation 56. As is generally the case, the channel does.notcompletely surround the casing. Fluid or gas will leak through channel55 trom the formation having the higher formation pressure to theformation having a lower formation pressure.

One method of stopping such leakage is to perforate casing 48 on theside of the casing where the leakage is occurring and force cementthrough the per:oration in the casing into the channel, thus blockingthe path of the leaking fluid. One problem in carrying out suchoperations is the difficulty in determining the direction in which theperforating device should be pointed so that the perforations are madeon the side of the casing behind which the channel has formed. Referringagain to FIG. 5, directional logger 40, perforating gun 57 with zerophasing, and downhole rotator barrel with rotation motor 32 aresupported in well 49 from electric wire line 16 for use in operations todetermine on which side of the casing the channeling has occurred.

As indicated above in the description of the preferred embodiment of thenoise logger, the two transducers are preferably spaced so that thecylindrical axes of the two transducers 11a and 11b are about six andone-half centimeters apart. Production tubing 50, however, may be toonarrow to allow a directional logger having transducers so spaced topass readily therethrough. As such, an alternate embodiment of thedirectional logger is used when the logger must be lowered throughnarrow production tubing. As shown in FIG. 6A, transducers 43a and 43bof directional logger 40 are pivotally mounted to arms 41a, and 41brespectively at pins 42a and 42b. The mechanical operation ofdirectional logger 40 is similar to the operation of the temperaturesensor assembly disclosed in U.S. Pat. No. 3,745,822, issued Jul. 17,1973 to Pierce et al., the entirety of which is incorporated herein byreference.

Arms 41a and 41b are attached to toothed cams 45a and 45b. These toothedcams rotate when rack 46 is moved vertically. When the logger is to belowered though the production tubing, the cams, rack, and thetransducers are in the position shown in FIG. 6A. The transducers areextended to their operating position in the same manner as the probes ofthe temperature sensor assembly disclosed in ierce are extended. Rack 46is moved downward within the tool. The operating mechanism for rack 46is not shown in FIG. 6A, and may be similar to that disclosed by Pierceor any other known system for operating such a mechanism in a boreholeenvironment. As rack 46 moves downward, cams 45a and 45b rotate to movearms 41a and 41b outward. The limit of rack travel is preset so that atthe end of its travel, the arms will have pivoted so that thecenter-to-center spacing between cylindrical transducers 43a and 43b, asmeasured at pins 42a and 42b, is about six and one-half centimeters. Asshown in FIG. 6B, spring 44 acts in combination with mechanical stops47a and 47b to bring the transducers into parallel alignment. The stopsare positioned so that spring 44 can pivot the bottom of the twotransducers about pins 42a and 42b no further than is required for suchparallel alignment.

Returning to FIG. 5, in operations to block leakage channel 55, logger40 is lowered through production tubing 50 with transducers 43a and 43bwithdrawn. When logger 40 has passed below the production tubing intothe area bounded only by casing 48, transducers 43a and 43b are extendedto their operating position. Noise logging operations like thosedescribed above are performed to locate the direction from which thenoise of the leakage through the channel is coming. However, for thisapplication, no absolute orientation measurement is required. Insteadthe logger 40 may be attached to or associated with the perforating gunso that when extended, as in FIG. 6B, a designated transducer, say 43ain FIG. 6B, is aligned with the shots 53 on the perforating gun 57.After the orientation of the minima axis is determined, then a rotationof either plus 90° or minus 90° will cause the signal from transducer43a to lead the signal from 43b. In this position, transducer 43a ispointed toward the channel 55 of FIG. 5, thereby orienting theperforation shots 53 toward channel 55.

It will be apparent that various changes may be made in the details ofconstruction of the apparatus and the details of the performance of themethods from those shown in the attached drawings and discussed inconjunction therewith without departing from the spirit and scope ofthis invention as defined in the appended claims. It is therefore to beunderstood that this invention is not to be limited to the specificdetails shown and described.

What is claimed is:
 1. A rotatable directional acoustic loggingapparatus for detecting noise from a source external to the apparatus,comprising:a first and a second cylindrical piezoelectric crystaltransducer positionable in a borehole spaced apart from each other in aplane substantially perpendicular to the longitudinal axis of saidborehole and with the cylindrical axes of the transducers substantiallyparallel to the longitudinal axis of said borehole, said transducersopposable to each other and capable of generating an output whilerotating simultaneously; and means for electrically prpocessing saidoutput to determine the amplitude and phase difference of the outputfrom the first and the second transducer, said means capable ofdetermining the direction of said noise by correlating the position ofminimum phase difference between the first transducer and the secondtransducer with the output which identifies the transducer leading inphase at a position 90 degrees from the osition of said minimum phasedifference.
 2. The apparatus of claim 1 wherein said first transducerhas a positive output lead electrically connected to the positive inputof an operational amplifier and said second transducer has a positiveoutput lead electrically connected to the negative input of saidamplifier so as to enable measurement of the amplitude and phase of thedifference in transducer outputs.
 3. The apparatus of claim 2 whereinthe output from the amplifier is fed over wire to a recorder.
 4. Theapparatus of claim 1 wherein the transducers are spaced so that theircylindrical axes are between about four centimeters and about eightcentimeters apart.
 5. The apparatus of claim 1 wherein the transducersare encapsulated in an epoxy block so as to maintain the desired spacingbetween the cylindrical axes of the transducers.
 6. The apparatus ofclaim 5 wherein said apparatus is adapted for lowering into a boreholeby being positioned in a conventional logging assembly supported on anelectric wire line.
 7. The apparatus of claim 1 further including anabsolute direction indicator.
 8. The apparatus of claim 7 wherein saidabsolute direction indicator is a gyroscope.
 9. The apparatus of claim 7wherein said absolute direction indicator is a magnetometer.
 10. Adirectional noise logging apparatus positioned in a logging assembly fordetecting noise from an external source, said apparatus supportable onen electric wireline and which can be lowered into a borehole havingnarrow production tubing, said apparatus comprising:a first and a secondcylindrical piezoelectric crystal transducer mounted on retractable armsconnected to said logging assembly so that the transducers may beretracted and lowered through said narrow production tubing into a widerdiameter lower borehole where the transducers may be extended to aposition spaced apart from each other in a plane substantiallyperpendicular to the longitudinal axis of said borehole and with thecylindrical axes of the transducers substantially parallel to thelongitudinal axis of said borehole, said crystal transducers opposableto each other and capable of generating an output while rotatingsimultaneously; and means for electrically processing said output todetermine the amplitude and phase difference of the output from thefirst and the second transducer said means capable of determining thedirection of said noise by correlating the position of minimum phasedifference between the first transducer and the second transducer withthe output which identifies the transducer leading in phase at aposition 90 degrees from the position of said minimum phase difference.11. The apparatus of claim 10 wherein the transducers are extendableuntil their cylindrical axes are at least about six and one-halfcetimeters apart.
 12. The apparatus of claim 10 wherein saidconventional logging assembly has a perforating gun with zero phaseshots associated with said apparatus such that the zero phase shots arein line with one of the transducers of said apparatus so that the shotsare oriented toward the noise direction when said gun is discharged. 13.A method for determining the direction of a subsurface noise from anexternal source, comprising the steps of:(a) lowering a logging assemblyon an electric wireline into a borehole of a well penetrating thesubsurface to a desired depth, said logging assembly including twopiezoelectric crystal transducers positioned spaced apart from eachother in a plane substantially perpendicularly to the longitudinal axisof said borehole and with the cylindrical axes of the transducerssubstantially parallel to the longitudinal axis of said borehole, saidtransducers held in position by a support attached to said loggingassembly; (b) generating an output from said transducers while saidtransducers are opposable to each other; (c) rotating said loggingapparatus through 360 degrees at said desired depth; (d) recording theoutput of said transducers during said rotation; (e) processing saidoutput to determine the amplitude and phase difference of the signalsfrom the first and the second transducer; (f) determining the directionof said noise by correlating the output identifying the position ofminimum phase difference between the first transducer and the secondtransducer with the output identifying the transducer leading in phaseat a position 90 degrees from the position of said minimum phasedifference.
 14. A directional logging method for determining thedirection of a noise source in a first well relative to a second wellremote therefrom comprising:(a) lowering to a desired depth into saidsecond well a directional acoustic logging apparatus positioned in alogging assembly having an absolute direction indicator, said loggingapparatus comprising two cylindrical piezoelectric crystal transducerselectrically opposable to each other each other and supported so that,at said desired depth, said crystals are substantially side by sidewithout touching and their cylindrical axes are substantially parallel;(b) generating an output from said crystal transducers to indicate theresponse of said crystal transducers to said noise source; (c) rotatingsaid noise logging apparatus and said absolute direction indicatorthrough 360 degrees; (d) recording the output of said directionallogging apparatus on phase and amplitude recording devices during saidrotation; (e) recording the output of said absolute direction indicatoron a recording device during said rotation; (f) correlating the outputrecorded on said phase and amplitude recording devices with the outputrecorded on said absolute direction recording device to determine theposition of the noise logging apparatus when its phase and amplitudeoutput are at a minimum; (g) observing which of the transducers isleading in phase when said logger is rotated 90° from said position toindicate the direction of said source.
 15. The method of claim 14 wheresaid desired depth that said logging apparatus is lowered into saidsecond well is the depth at which the peak amplitude noise output ofsaid logging apparatus occurs.
 16. The method of claim 15 where saidpeak amplitude noise output is determined by repeating said rotating ofthe apparatus and recordings of its output at various depths in thewell.